The present invention concerns an improved electric stop motion apparatus for a textile machine fed with fibre slivers, in particular for a drawframe, containing a pan or rocker for each input sliver, which pan is tiltable between a working position and a stop position, tilting of such pan being effected by the running out of the fibre sliver and serving to activate an electric stop motion contact.
In textile machines fed with fibre slivers, such as e.g. drawframes, a plurality of fibre slivers are withdrawn from creel cans and are supplied to the drafting arrangement via a feed table, on which the fibre slivers are carefully lined up side by side. If only one of the fibre slivers to be supplied is absent for any reason, e.g. because the corresponding creel can is empty, or because the fibre sliver supply is interrupted, the machine is to be stopped immediately, in order to avoid production of faulty fibre sliver, i.e. of a fibre sliver with too small a weight. The stopping action furthermore is to be effected within a very short time, in such a manner that the end of the sliver running out cannot be taken-in into the drafting arrangement. As long as the end of the sliver still is located on the feed table, the leading end of a new sliver can be connected manually to the end running out, which is effected by "piecing", in such a manner that no faulty portion is produced in the fibre sliver delivered from the machine. If this is not the case, however, i.e. if the sliver end running out reaches, or passes through, the drafting arrangement, before the sliver breakage is detected and the machine is stopped, a certain fibre sliver portion of lower fibre content unavoidably is produced, which portion is to be eliminated, if no risk of production of faulty finished products (woven or knitted fabrics, etc.) is to be taken into account. Furthermore the insertion of the new sliver leading end in the drafting arrangement is an operation which is much more complicated and time-consuming than the above mentioned "piecing".
Thus, numerous stop motion devices were developed during the course of time, and the continuing increase in the operating speeds imposing more demanding requirements, particularly with respect to the reaction speeds required.
The various known devices of this type, of which as an example the device according to the German Pat. No. 909,550 is mentioned, function according to the principle of sliver detection using a feeler lever. In the absence of a sliver the lever can move from an operating position, in which the lever is supported by throughpassing sliver, to a stopping position, usually by performing a tilting movement, this movement being used for activating an electric stopping contact.
In the above mentioned solution according to the German Pat. No. 909,550 the throughpassing fibre sliver is detected using a pan-type flap which is tiltable to one side, which activates the stopping switch, and which from below is held in contact with the throughpassing fibre sliver by using a tongue. Similar solutions using direct detection of the throughpassing sliver are known in great numbers, in which the sliver is detected from above, instead of from below as in the patent mentioned here. As an example of a device using detection from above, there is to be mentioned for instance U.S. Pat. No. 3,305,896.
All these known solutions show considerable disadvantages stemming from the direct feeler detection. These disadvantages are, among others:
(a) Formation of so-called "fibre beards" on the feeler lever. In the margin zones of the feeler element, which no longer are sufficiently swept by the throughpassing sliver, i.e. where the contacting pressure is lowest, fibres can cling, for which smallest rough spots are sufficient, which eventually lead to fibre accumulations. Such accumulations from time to time are released and are carried on by the sliver, in such a manner that a fault is generated in the sliver which is produced.
(b) Such feeler elements swept by the material are subject to contamination by fibre and dust particles contained in the material itself, which contamination can impair the reliability of the stop motion device. Since fibre slivers as a rule cannot withstand high tensile stresses, the feeler elements necessarily are to be designed as elements functioning under feable forces. Small changes in the frictional properties of the feeler lever thus already can influence the activation susceptibility of the stop motion device, the stopping function thus becoming unreliable.
(c) There is a dependency upon the type of material which is processed, particularly upon its volume. It is well known that fibre slivers of the same weight can differ considerably in their cross-section areas, depending on e.g. the degree of crimp and parallelism of the fibres, but also on the degree of compression the slivers undergo, as they are deposited in cans. Thus, in sliver-feeling stop motion devices adaptations to the material which is being processed may possibly prove necessary for ensuring optimum working conditions.